This invention relates to a process for the production of a particularly thin-walled body of revolution, consisting of a pipe and a dish-shaped, convex bottom, for example for an internal pressure vessel. This body of revolution generally does not rotate about its axis, but rather is to be understood to mean, in this connection, a body of revolution or rotation which can be constructed in accordance with Guldin's rule.
It has been contemplated to manufacture a pipe and bottom, as indicated above, separately from each other, and then to weld these parts together to form the aformentioned body of revolution. This is relatively complicated and expensive. Also, this body of revolution in this case shows an interruption in its smooth line of material. The welding bond and/or the welding seam is not very desirable in most cases. However, a production of the body of revolution, for example, by turning from a solid material requires a large quantity of starting material and is likewise complicated and costly.
It is an object of this invention to produce the body of revolution with a much smaller amount of starting material from a single piece.
This object is attained, according to the invention, by producing a dish-shaped blank, adapted to the configuration of the aforementioned bottom, by means of a non-cutting shaping method; providing this blank, by a turning operation, with a turned bottom portion deformable by stretching to obtain this bottom or the respective bottom portion and with an adjoining turned tubular portion deformable by stretching to obtain the aforementioned pipe; and producing the above-mentioned body of revolution by stretching these two turned portions.
For the manufacture of this blank of a metal, particularly steel, but also aluminum, by a non-cutting shaping operation, especially by forging, preferably drop forging, a much smaller quantity of starting material is required than for the turning of the body of revolution from a solid piece. This is so because the wall thickness of the dish-shaped blank is relatively minor and its required axial extension is relatively small. This blank can be produced, due to its relatively minor axial extension, by a non-cutting shaping step, especially by drop forging. Additional advantages of the invention reside in that a great dimensional accuracy of the body of revolution is attained, that this body does not show an interruption in the smooth line of material at the transition from the bottom to the tubular section, and does not show a welding bond or seam, either, at that point; and that the expenditures for material and production are relatively minor and the method is uncomplicated. The process of this invention makes it possible to manufacture an extremely lightweight body of revolution.
A stretching step as mentioned above refers especially to a cold-forming method, for example if a blank of steel is involved, and to a hot-forming process, for example in case of a blank of titanium.
The following embodiments of the process of this invention render this process even more advantageous, in particular increase the above-mentioned dimensional accuracy, improve the smooth line of the material at the aforementioned transition zone, and even further reduce the axial extension of the blank:
The stretching of the turned bottom portion is, in particular a projection stretching process, which is also called a projection stretch-forming pressing step. The stretching step for the tubular turned portion is especially a cold extrusion process. In particular, the turned bottom portion assumes, by the turning operation, the shape of an outwardly projecting bead and has a wall thickness increasing toward the turned tubular portion. The longitudinal cross-sectional area and the length of the bead are so large that, due to the stretching step, the desired wall thickness and curved length of the bottom and/or the associated bottom portion are attained. The turned bottom portion is stretched, in particular, by means of a pressure or stretching mandrel and by means of pressure or stretching rollers. Advantageously, the above-mentioned bead is fashioned, by the turning operation, with a shoulder for the engagement of pressure or stretching rollers. This has the result that the material, starting right from the stretching step, flows and is not ruptured. However, due to the turning operation, the turned pipe portion is provided, in particular, with a uniform wall thickness. In most cases, this wall thickness is larger than the maximum wall thickness of the above-mentioned bead. This wall thickness is so large that, together with the length of the turned tubular portion, the desired wall thickness and length of the pipe are obtained by the stretching process. In most instances, the volume of the turned tubular portion is selected so that, after stretching, the wall thickness of this tube (pipe) is as large or approximately as large, as the wall thickness of the bottom or bottom portion. However, the volume can also be chosen so that, after stretching, the wall thickness of the pipe is twice as large, or approximately twice as large, as the wall thickness of the bottom or bottom portion. This is of special importance for the manufacture of internal pressure vessels, which will be explained below.
A process according to the invention for the production of a container by means of the process of this invention as set out hereinabove resides in that two above-mentioned bodies of revolution, having the same pipe diameter, are manufactured, and the two pipes thereof are joined at their end faces with each other by welding or soldering. The thus-obtained container has only a single weld seam. Furthermore, a process of this invention for the manufacture of a container from a body of revolution produced according to the process of this invention resides in that the body of revolution is provided, at its open end, with a likewise dish-shaped, convex bottom, by joining this bottom and the pipe via their end faces with each other by means of welding or soldering. The thus-obtained container likewise has only a single weld seam.
In both cases, the welding step is preferably an electron beam welding procedure, since the high dimensional accuracy attained by the process of this invention ensures a satisfactory bond by means of electron beam welding. For example, tolerances of less than 0.04 mm. can be obtained at a pipe diameter of approximately 300 mm. and a pipe wall thickness of 2 mm.
According to an aforementioned container manufacturing method, an internal pressure vessel can also advantageously be produced by utilizing especially that aforementioned embodiment of the process, according to which the wall thicknesses of the pipe and of the bottom are the same, or approximately the same, and wherein the two pipes and/or the pipe, after this welding or soldering bonding step, are and/or is provided with a wound jacket of fiber-reinforced synthetic resin or wire, absorbing at least part of the internal pressure. This jacket is preferably so strong and/or so firm and so thick that it absorbs about 50 % of the internal pressure and/or the internal pressure forces, while the pipes or pipe likewise absorb or absorbs about 50%. This is very advantageous, because the body of revolution having identical wall thicknesses of its pipe and its bottom can be manufactured at low expenditure and with a very smooth flow of the line of material at the transition from the bottom to the pipe-shaped portion. At the same internal pressure, without this jacket, however, the wall thickness of the pipe must be about twice as large as that of the bottom. If desirable or necessary, the two bottoms can additionally be provided with a wound jacket of the aforementioned type, absorbing at least part of the internal pressure. The internal pressure of the container, which can be relatively high, can stem from a gaseous or liquid medium which is to be housed in the container. The above-mentioned fiber-reinforced synthetic resin is preferably a carbon-fiber-reinforced plastic. Such an aforementioned body of revolution or container is intended, for example, for the reception of a gaseous or liquid medium in an automotive vehicle, an aircraft, or a space vehicle.
The bottom of the body of revolution is preferably hemispherical, but it can also have some other configuration, such as a semielliptic shape, or the like, for example.